To Know the Dark
To go in the dark with a light is to know the light.
To know the dark, go dark. Go without sight,
And find that the dark, too, blooms and sings,
And is traveled by dark feet and dark wings.
                                                  —Wendell Berry

If you live in or near a city, chances are you don’t see many twinkling little stars at night because light pollution — the fastest growing form of human-caused pollution — is making the night sky glow brighter each year. In fact, night skies across roughly half of the U.S. are polluted by artificial light. A fairly recent study from the University of Exeter found that observable light emissions increased globally by at least 49 percent from 1992 to 2017. But that figure only includes light visible via satellites, and scientists estimate the actual increase may be much higher — as much as 270 to 400 percent, depending on  the region.

Excessive, poorly designed lighting that spills skyward changes the predictable day/night cycle that life evolved in. Even tucked into bed, our glaring human footprint trespasses into the nocturnal world to mess up biological rhythms and health, consume and waste energy, steal the beauty and wonder of the nighttime sky, contribute to climate change, and disrupt beings within complex ecosystems. 

As I wrote in a Portland Monthly article a few years ago, myriad wildlife species that work the dusk and dawn or graveyard shifts depend on uninterrupted darkness to provide exquisitely timed cues that direct communication, reproduction, protection, sleep, foraging behavior, and orientation. For long-distance migratory birds who travel at night during spring and fall using celestial navigation, artificial light can disrupt or kill them in several ways. The timing of migration (when wildlife leave their summer or winter grounds) is controlled by several factors, one of which is photoperiod (the duration of light and dark), a predicable indicator of time of year. When the haze of artificial lighting conceals this cue, birds may leave too early or too late, which may cause them to miss optimal nesting conditions. And when lured into a maze of city lights, migrants become confused and disoriented and often collide with unnecessarily illuminated buildings, or drop from exhaustion. It’s estimated that as much as a billion birds are killed this way each year in North America, but it’s not only birds that are affected.

Nocturnal moth (Cyclophora pendulinaria), awaiting the dark.

All animals—reptiles (including sea turtles), amphibians, mammals (including humans)—are negatively impacted. Arthropods, like nocturnal moths — their fate seamlessly interconnected with other ecosystem members — perish rather than pollinating, breeding, and supplying food for birds. And the seasonal cycle of plants, including trees — particularly those with the misfortune of being planted beneath streetlights or in the path of landscape lighting — is threatened. Researchers believe that early bud break caused by incessant light will have a cascade effect on other organisms whose life cycles work in tandem with such plants, as well as the plants themselves. A recent study suggests that intensified light at night may have serious far-reaching consequences in disruption of key ecosystem functions and services.

Plants need to “sleep” in darkness, just as we do, and sleep deprivation is as harmful to trees as it is to animals. Trees that are sensitive to day length tend to be more affected by artificial light, and changes to day length can cause disruptions in flowering patterns, growth of larger leaves (which can cause them to be more susceptible to air pollution or water stress), and even prevent trees — particularly young ones — from entering dormancy in autumn. Longer growing seasons are not a good thing! Tree species most affected by artificial light include dogwood, maple, birch, aspen and cottonwood.

The bright side
Although nights are getting brighter each year since continual development and sprawl amplify light pollution, there is a bright side: It’s reversible. Organizations such as the International Dark-Sky Association and many smaller groups, like Audubon of Portland’s Lights Out campaign, are working to preserve and protect the night skies, and there are Dark Sky communities, parks, and preserves. While it will take urban planners, designers of fixtures and buildings, and elected local officials to create standards for outdoor lighting that minimizes light pollution, glare and trespass overall, those of us who are homeowners can each do our part—and it takes very little effort. 

Hello darkness, my old friend
→ Switch it off: Turn off unnecessary outdoor lights or, better yet, install motion-sensors that are designed to turn on only when needed and turn off after a short period of time.
→ Shield it: Use fixtures that aim light downward and that are shielded to prevent glare and “trespass” on habitat and neighbors. Those that have a solid cap above the bulb that prevents light from traveling skyward are best; you can also buy shades to fit existing fixtures. Lowering fixtures sometimes can also help.
→ Warm it up: Select warm-colored LEDs (under a 3,000 Kelvin rating) that supply only the amount of light needed. Those that emit short cool or blue wavelengths are brighter, scatter light more, and are worse for wildlife.
→ Remember indoor lights: Close draperies, especially during peak migration seasons (April through June and August through November) to stop rays from straying outdoors.
→ Request shields: Shields on streetlights may be possible. Inquire with your local department of transportation.
→ Buck the trend of landscape lighting: Most “decorative” outdoor lighting is pointless, detrimental to wildlife and plants, and wasteful, particularly fixtures that point light upwards and sideways.
→ Close all blinds, shades and/or shutters to reduce nighttime light that attracts and confuses wildlife.

Safety concerns?
Most home burglaries occur in broad daylight, not in the middle of the night, and excessive lighting does not lessen crime. In fact, studies show that bright lights can make victims and property easier to see, as well as create much greater contrast and excessive glare, which increases the deep shadows that may actually increase crime and vandalism and make it more difficult to see potential intruders on your property. To improve security, use motion sensors that don’t give criminals a leg up. 

© 2018 Eileen M. Stark

Updated 02/2024